Determining wind loading of structures through wind flow simulation

ABSTRACT

A method, system, apparatus, article of manufacture, and computer readable storage medium provide the ability to automatically simulate a wind load. An analytical model is converted into a solid model. A wind flow on the solid model is simulated to determine pressures on structural elements of the solid model. The simulating is repeated until the pressures converge. The pressures are converted to loads on the structural elements. Load cases are generated with equivalent loads on the structural elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to structural engineering anddesign, and in particular, to a method, apparatus, and article ofmanufacture for determining wind load structure.

2. Description of the Related Art

Engineers must design structures to withstand the loading that thestructure will experience. One of the more difficult loadings that theengineer must account for is the effect wind will have when interactingwith the structure. Flowing air will create pressure, both positive andnegative, when it encounters a structure and interacts with it. Flowpatterns are determined by the shape of the structure, and directionthat the flowing air comes from. Understanding these interactions andthe behavior of the air when interacting with the structure is a complexand time consuming task. Engineers often must rely on expensive and timeconsuming physical testing for all but the most simple geometries. Tobetter understand the problems of the prior art, a description of windloads and prior art approaches to determining the effect of wind may behelpful.

When designing structures, structural engineers must account for theeffect of different loads/forces that may affect the structure.Different loads/forces cause a structure to move in different ways. Forexample, gravity loads (e.g., people walking on a structure, furniturein/on a structure, etc.) create a downward load. Loads applied in asideways orientation (parallel to the ground) may cause a structure tomove laterally. Two movements require a structure to have lateralreinforcement: (1) seismic movement (i.e., ground movement); and (2)wind that creates loads causing a building to move laterally.Accordingly, an important consideration for structural engineers is todesign a structure with appropriate lateral reinforcement to withstandthe effect of wind loads.

Designing a structure to account for different loads is a time consumingaspect of an engineering workflow. Every type of structure is windexposed. Further, many different load cases have to be considered (asthe value and direction of wind may differ). Prior art systems oftenapply simplified methods to different structure types. In many products,some national codes provide requirements that are used. In other words,load cases are based on building codes promulgated by localjurisdictions. Such prior art methods may be partially automated but arelimited to specific structures or geometry types. Further, prior artsolutions are very often insufficient for complicated structures. Morespecifically, for a lot of structure types, the wind load is the mostsignificant load type (e.g., buildings with broad roofs and walls,masts, truss towers, silos, etc.). If the structure consists of a normalshaped building (e.g., rectangular multi-story structure), the code mayprovide details regarding how to apply load (e.g., based on exposureclass and a number of other factors). However, when the geometry is notregular, the engineer must manually determine how the wind will affect astructure (e.g., what happens with flow patterns, where is positivepressure created, where is negative pressure created, etc.). Withcomplicated geometry, determining the different wind load cases can beexpensive and difficult.

With complex structures that fall outside of the standard codes,engineers attempt to create various load cases and guestimate as bestthey can during the building design. This process involves the manualtime consuming creation of load cases (e.g., based on many rules,guidelines, and building codes). Thereafter, a model is created. Inpractice, the load case and model creation may simplify the geometrythereby resulting in overloading or overlooking various aspects. Anexpensive and time-consuming wind tunnel study is then conducted. Inthis regard, a physical prototype may be constructed, access to a windtunnel is required and needs to be paid for, results are analyzed,results are correlated with the design, and the analysis is then scaledin order to determine the loads that are applied to the structure.Accordingly, limitations of a real wind tunnel testing includes not onlyhigh costs but also a time consuming process. Further, in many cases,understanding wind loads effects is significant even in the early stageof design, and can drive design stages. Unfortunately, wind tunneltesting often occurs at the later stages of the design process.

In view of the above, prior art systems for determining and analyzingwind loads are time consuming, expensive, and prone to error based onthe extensive manual calculations and analysis that are performed. Priorart systems fail to provide any automation, fail to provide flowanalysis, and fail to use computational fluid dynamics in order tounderstand the effects of wind on a structure.

SUMMARY OF THE INVENTION

Embodiments of the invention overcome the problems of the prior art bycreating a virtual wind tunnel that may be used to provide an engineerguidance on how a structure will impact flow of the wind and create theconditions around the building as well as how the wind itself willimpact the structure. Accordingly, wind simulation may be used forvarious model types including buildings, bridges, tresses, stadiums, andsteel structures (e.g., supporting platforms, towers, etc.). Usingcomputational fluid dynamics, pressures exhibited on a structure may beautomatically and quickly predicted. Such pressures are automaticallyconverted to load cases that may be used in the analysis of thestructure itself.

Accordingly, embodiments of the invention may be used to validate manualload generations, automatically generate wind loads, provide earlyfeedback during the design process, and may be used for any model type.Further, such wind load generation and analysis is automatic and fast.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is an exemplary hardware and software environment used toimplement one or more embodiments of the invention;

FIG. 2 schematically illustrates a typical distributed computer systemusing a network to connect client computers to server computers inaccordance with one or more embodiments of the invention;

FIG. 3 is a flow chart illustrating the logical flow for automaticallysimulating wind loads in accordance with one or more embodiments of theinvention;

FIGS. 4A and 4B illustrate various window tabs of an exemplary dialogthat may be used to set wind simulation parameters in accordance withone or more embodiments of the invention;

FIG. 5 illustrates a wind simulation progress monitor in accordance withone or more embodiments of the invention;

FIG. 6 illustrates the different edges and panels that may be used tocompute linear loads in accordance with one or more embodiments of theinvention; and

FIG. 7 illustrates the equilibration of a model in accordance with oneor more embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which form a part hereof, and which is shown, by way ofillustration, several embodiments of the present invention. It isunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

Hardware Environment

FIG. 1 is an exemplary hardware and software environment 100 used toimplement one or more embodiments of the invention. The hardware andsoftware environment includes a computer 102 and may includeperipherals. Computer 102 may be a user/client computer, servercomputer, or may be a database computer. The computer 102 comprises ageneral purpose hardware processor 104A and/or a special purposehardware processor 104B (hereinafter alternatively collectively referredto as processor 104) and a memory 106, such as random access memory(RAM). The computer 102 may be coupled to, and/or integrated with, otherdevices, including input/output (I/O) devices such as a keyboard 114, acursor control device 116 (e.g., a mouse, a pointing device, pen andtablet, touch screen, multi-touch device, etc.) and a printer 128. Inone or more embodiments, computer 102 may be coupled to, or maycomprise, a portable or media viewing/listening device 132 (e.g., an MP3player, iPod™, Nook™, portable digital video player, cellular device,personal digital assistant, etc.). In yet another embodiment, thecomputer 102 may comprise a multi-touch device, mobile phone, gamingsystem, internet enabled television, television set top box, or otherinternet enabled device executing on various platforms and operatingsystems.

In one embodiment, the computer 102 operates by the general purposeprocessor 104A performing instructions defined by the computer program110 under control of an operating system 108. The computer program 110and/or the operating system 108 may be stored in the memory 106 and mayinterface with the user and/or other devices to accept input andcommands and, based on such input and commands and the instructionsdefined by the computer program 110 and operating system 108, to provideoutput and results.

Output/results may be presented on the display 122 or provided toanother device for presentation or further processing or action. In oneembodiment, the display 122 comprises a liquid crystal display (LCD)having a plurality of separately addressable liquid crystals.Alternatively, the display 122 may comprise a light emitting diode (LED)display having clusters of red, green and blue diodes driven together toform full-color pixels. Each liquid crystal or pixel of the display 122changes to an opaque or translucent state to form a part of the image onthe display in response to the data or information generated by theprocessor 104 from the application of the instructions of the computerprogram 110 and/or operating system 108 to the input and commands. Theimage may be provided through a graphical user interface (GUI) module118. Although the GUI module 118 is depicted as a separate module, theinstructions performing the GUI functions can be resident or distributedin the operating system 108, the computer program 110, or implementedwith special purpose memory and processors.

In one or more embodiments, the display 122 is integrated with/into thecomputer 102 and comprises a multi-touch device having a touch sensingsurface (e.g., track pod or touch screen) with the ability to recognizethe presence of two or more points of contact with the surface. Examplesof multi-touch devices include mobile devices (e.g., iPhone™, Nexus S™,Droid™ devices, etc.), tablet computers (e.g., iPad™, HP Touchpad™),portable/handheld game/music/video player/console devices (e.g., iPodTouch™, MP3 players, Nintendo 3DS™, PlayStation Portable™, etc.), touchtables, and walls (e.g., where an image is projected through acrylicand/or glass, and the image is then backlit with LEDs).

Some or all of the operations performed by the computer 102 according tothe computer program 110 instructions may be implemented in a specialpurpose processor 104B. In this embodiment, the some or all of thecomputer program 110 instructions may be implemented via firmwareinstructions stored in a read only memory (ROM), a programmable readonly memory (PROM) or flash memory within the special purpose processor104B or in memory 106. The special purpose processor 104B may also behardwired through circuit design to perform some or all of theoperations to implement the present invention. Further, the specialpurpose processor 104B may be a hybrid processor, which includesdedicated circuitry for performing a subset of functions, and othercircuits for performing more general functions such as responding tocomputer program 110 instructions. In one embodiment, the specialpurpose processor 104B is an application specific integrated circuit(ASIC).

The computer 102 may also implement a compiler 112 that allows anapplication or computer program 110 written in a programming languagesuch as COBOL, Pascal, C++, FORTRAN, or other language to be translatedinto processor 104 readable code. Alternatively, the compiler 112 may bean interpreter that executes instructions/source code directly,translates source code into an intermediate representation that isexecuted, or that executes stored precompiled code. Such source code maybe written in a variety of programming languages such as Java™, Perl™,Basic™, etc. After completion, the application or computer program 110accesses and manipulates data accepted from I/O devices and stored inthe memory 106 of the computer 102 using the relationships and logicthat were generated using the compiler 112.

The computer 102 also optionally comprises an external communicationdevice such as a modem, satellite link, Ethernet card, or other devicefor accepting input from, and providing output to, other computers 102.

In one embodiment, instructions implementing the operating system 108,the computer program 110, and the compiler 112 are tangibly embodied ina non-transitory computer-readable medium, e.g., data storage device120, which could include one or more fixed or removable data storagedevices, such as a zip drive, floppy disc drive 124, hard drive, CD-ROMdrive, tape drive, etc. Further, the operating system 108 and thecomputer program 110 are comprised of computer program 110 instructionswhich, when accessed, read and executed by the computer 102, cause thecomputer 102 to perform the steps necessary to implement and/or use thepresent invention or to load the program of instructions into a memory106, thus creating a special purpose data structure causing the computer102 to operate as a specially programmed computer executing the methodsteps described herein. Computer program 110 and/or operatinginstructions may also be tangibly embodied in memory 106 and/or datacommunications devices 130, thereby making a computer program product orarticle of manufacture according to the invention. As such, the terms“article of manufacture,” “program storage device,” and “computerprogram product,” as used herein, are intended to encompass a computerprogram accessible from any computer readable device or media.

Of course, those skilled in the art will recognize that any combinationof the above components, or any number of different components,peripherals, and other devices, may be used with the computer 102.

FIG. 2 schematically illustrates a typical distributed computer system200 using a network 204 to connect client computers 202 to servercomputers 206. A typical combination of resources may include a network204 comprising the Internet, LANs (local area networks), WANs (wide areanetworks), SNA (systems network architecture) networks, or the like,clients 202 that are personal computers or workstations (as set forth inFIG. 1), and servers 206 that are personal computers, workstations,minicomputers, or mainframes (as set forth in FIG. 1). However, it maybe noted that different networks such as a cellular network (e.g., GSM[global system for mobile communications] or otherwise), a satellitebased network, or any other type of network may be used to connectclients 202 and servers 206 in accordance with embodiments of theinvention.

A network 204 such as the Internet connects clients 202 to servercomputers 206. Network 204 may utilize ethernet, coaxial cable, wirelesscommunications, radio frequency (RF), etc. to connect and provide thecommunication between clients 202 and servers 206. Clients 202 mayexecute a client application or web browser and communicate with servercomputers 206 executing web servers 210. Such a web browser is typicallya program such as MICROSOFT INTERNET EXPLORER™, MOZILLA FIREFOX™,OPERA™, APPLE SAFARI™, GOOGLE CHROME™, etc. Further, the softwareexecuting on clients 202 may be downloaded from server computer 206 toclient computers 202 and installed as a plug-in or ACTIVEX™ control of aweb browser. Accordingly, clients 202 may utilize ACTIVEX™components/component object model (COM) or distributed COM (DCOM)components to provide a user interface on a display of client 202. Theweb server 210 is typically a program such as MICROSOFT'S INTERNETINFORMATION SERVER™.

Web server 210 may host an Active Server Page (ASP) or Internet ServerApplication Programming Interface (ISAPI) application 212, which may beexecuting scripts. The scripts invoke objects that execute businesslogic (referred to as business objects). The business objects thenmanipulate data in database 216 through a database management system(DBMS) 214. Alternatively, database 216 may be part of, or connecteddirectly to, client 202 instead of communicating/obtaining theinformation from database 216 across network 204. When a developerencapsulates the business functionality into objects, the system may bereferred to as a component object model (COM) system. Accordingly, thescripts executing on web server 210 (and/or application 212) invoke COMobjects that implement the business logic. Further, server 206 mayutilize MICROSOFT'S™ Transaction Server (MTS) to access required datastored in database 216 via an interface such as ADO (Active DataObjects), OLE DB (Object Linking and Embedding DataBase), or ODBC (OpenDataBase Connectivity).

Generally, these components 200-216 all comprise logic and/or data thatis embodied in/or retrievable from device, medium, signal, or carrier,e.g., a data storage device, a data communications device, a remotecomputer or device coupled to the computer via a network or via anotherdata communications device, etc. Moreover, this logic and/or data, whenread, executed, and/or interpreted, results in the steps necessary toimplement and/or use the present invention being performed.

Although the terms “user computer”, “client computer”, and/or “servercomputer” are referred to herein, it is understood that such computers202 and 206 may be interchangeable and may further include thin clientdevices with limited or full processing capabilities, portable devicessuch as cell phones, notebook computers, pocket computers, multi-touchdevices, and/or any other devices with suitable processing,communication, and input/output capability.

Of course, those skilled in the art will recognize that any combinationof the above components, or any number of different components,peripherals, and other devices, may be used with computers 202 and 206.

Software Embodiment Overview

Embodiments of the invention are implemented as a software application(such as a wind load simulation application) on a client 202 or servercomputer 206. Further, as described above, the client 202 or servercomputer 206 may comprise a thin client device or a portable device thathas a multi-touch-based display.

Embodiments of the invention provide a method to generate wind loads onany type of structure. The method is based on a simulation of the windflow using computational fluid dynamics. Wind loads are createdautomatically based on pressures generated on elements during asimulation process. In particular, elements of the invention include:

a computation fluid dynamics engine used to simulate a wind flow;

automatic simulation parameters set according to a structure size(resolution, bounding box);

conversion of a structural model to a solid model used in a simulationprocess;

applying wind parameters to a structure and simulation (wind speed,elements, selection, wind profile, wind directions, etc.);

a method to check a convergence process during the simulation;

automatic pressure transfer from the solid model to structural elements(wall, columns, etc.);

automatic loads generation based on the convergence factor; and

automatic generation of load cases for different wind directions.

As used herein, the term “automatic” and “automated” provide forperforming the action without further/additional user input.

Wind Load Simulation Logical Flow

Automatic wind loads/load cases generation is a completely new approachto defining wind loads. Relying on a simulation engine that allows themodeling of wind flow, it is possible to build a tool that isindependent from a code (e.g., building code) based approach. Asdescribed above, for complicated structures, with advanced geometry,it's often very tough to calculate wind loads. Wind loads generation,based on wind simulation gives a user the possibility to use software asa substitute for use of a physical wind tunnel. Results from anautomatic wind generation may be used to conduct further analysis or asa double-check of a typical (based on codes) approach.

Embodiments of the invention utilize a solver (also referred to hereinas a simulation engine) inside a structural analysis application (e.g.,Robot Structural Analysis (RSA) Professional™ available from theassignee of the present application). Rather than merely observing windflow, embodiments of the invention generate wind loads on structureelements based on the wind flow. Further, a solver may be utilized withpredefined settings that are optimally set, taking into account speedcalculations (performance) and result accuracy. In addition, thestructural analysis application may be linked with computational fluiddynamics (CFD) to provide an advanced analysis tool for fluid analysis.Further, a structural analysis model/process may be saved in anappropriate format while flow analysis may be performed in/by a CFDengine/tool.

FIG. 3 is a flow chart illustrating the logical flow for automaticallysimulating wind loads in accordance with one or more embodiments of theinvention.

At step 300, the wind load simulation process starts.

At step 302, the analytical model containing the structure is convertedto a solid model. Typically, analytical models are merely 2D structuresand/or are not solid models in terms of geometry. In contrast,embodiments of the invention convert a structure to a solid modelconsisting of 3D volumes/elements. This step includes the creation of ageometric representation of a structural system within a structuralanalysis application. The geometric representation is referred to as ananalytical model. The analytical model represents various elements suchas beams, columns, floor plates, cladding elements, etc. of a buildingthat perform structural work/support for the building. The analyticalmodel is then converted to the solid model.

Properties/parameters that may influence how the elements behave (e.g.,shape, grade of steel, etc.) may also be assigned to the variouselements of the solid model. Such parameters may identifywhether/where/which openings (in the structure/model) are treated asopen (e.g., an open window) and/or closed (a window that isclosed/sealed with glazing). Determining whether an element is to betreated as open or closed determines whether to include such elements inthe structural/wind flow analysis/simulation and determines whetherthere is interior wind flow/pressures that need to be analyzed. As anexample, wind may flow through a structure that is open (e.g., a parkingstructure) (thereby creating interior wind flow and pressures) whilewind flow may flow around a closed structure (e.g., a residential towerthat has windows and doors and no internal wind flow).

In addition to the above, flow may be influenced by a terrain andsurrounding structures. As used herein, “terrain” refers to the naturalstate of the land, while man made objects that might influence the flowfalls outside of such terrain. For example, a funneling or channelingeffect of window flow may result in a cityscape (e.g., wind in an alleyor due to tall buildings). In this regard, structures may direct wind indifferent directions and the effects may be amplified based on theterrain/structures. To account for such an effect, embodiments of theinvention provide for the automatic generation of terrain and/orstructure(s) (that allow a user to simulate a real surrounding of astructure). There are two methods for this option. A first method is afree modeler that allows the simulation of surroundingbuildings/structures. Such a method may be a random terrain/structuregeneration method where an object/geometry/structure/terrain is createdthat mimics the effect that one would find at a physical site.Alternatively, a second method automatically reads an area(buildings/structures/terrain) from maps. In other words, actual datafrom a physical location/site may be used to provide suchterrain/structures. For example, data/information from a 3D mappingapplication (e.g., Google Earth™) may be leveraged to create theterrain/structures. More specifically, the map data from the actuallocation where a building under design is to be placed may be utilizedto acquire surrounding data that may affect/impact wind flow.

Further to the above, embodiments of the invention may provide for theautomatic generation of a façade for a structure. As a structuralengineer, the structure/structural system is often modeled withoutregard to the exterior of the structure. However, as described herein,the exterior (also referred to as the exterior skin) of a structure iswhat affects wind flow. Accordingly, embodiments of the inventionautomatically enclose (or add an exterior skin) to a structure based onthe frame of the structure rather than manually modeling the exterior.Such an automated façade generation assists the engineer by adding andattaching exterior panels to a structure's foundation/structuralelements so that wind simulation may be performed. Further, such amethod allows a user to quickly generate non-structural elements thattransfer wind loads to a structural frame.

A further enhancement may include the automatic generation of icing(e.g., the automatic change of an element's volume). In an industrialstructure with open lattice such as a transmission tower (e.g., builtout of steel girders), ice may build upon the elements therebyincreasing their volume (i.e., the area of the structure that catchesthe wind). Embodiments of the invention provide an automated mechanismfor increasing the area based on ice build-up. Such a mechanism mayincrease the geometry of the structure based on an icing condition.

At some point, engineers need to determine the wind load on a structure.In this regard, the engineer takes the analytical model they havedeveloped and creates a scenario where a virtual wind tunnel is used tounderstand the effects of wind on the structure.

At step 304, the simulation process starts.

At step 306, wind flow is simulated. Such a wind flow simulation mayinclude establishing a virtual bounding box around the designedstructure. Based on the size of the structure, such a bounding box maybe determined programmatically. To perform the wind flow simulation, theanalytical model along with parameters that describe the flow of thewind (e.g., wind speed and direction) are passed onto the solver. Thesolver interprets the data in terms of how the flow proceedsaround/through the structure. Further, the solver determines thepressure that is generated at a particular surface by the impact of thewind. Accordingly, the input to a solver includes the geometry (and flowcharacteristics) as well as parameters that define the flow of thewind/airstream. Output from the solver include the pressures on thesurface of the model. Such simulations are typically run in the cardinaldirections (e.g., East, West, North, South) of a structure/project. Inthis regard, the simulating may be sequentially performed in multiplecardinal directions. Alternatively, the simulating may be performedsimultaneously and in arbitrary (not only cardinal) directions. Asdescribed herein, the convergence of each simulating is performed, andtherefore, the automation of these multiple tasks is possible.

When configuring the simulation, embodiments of the invention may enablethe ability to define different wind factors for different winddirections. In other words, a wind profile may be configured wheredifferent parameters may be applied to different directions (e.g., astronger wind coming out of the West). Such a wind profile may alsoenable the user to define wind speed/direction for different heights.For example, the following wind speeds may be defined: 60 mph for anelevation of 0 feet to 50 feet; 70 mph for an elevation of 50 feet to100 feet; and 100 mph for elevations over 100 feet. An exemplarygraphical user interface for defining such a wind profile is describedin further detail below.

An additional enhancement to the wind simulation enables the automatedconfiguration of wind profiles depending on terrain and/or exposurecategory. In the prior art, an engineer examines a map as part of abuilding code. Such a wind map provides historical data that determinesthe wind speed that a structural engineer must design for. However, theexposure class (e.g., near open water, open fields, hilly terrain, denseurban area, etc.) may further affect the wind speed. Embodiments of theinvention automatically generate wind profiles for a user based ondifferent codes for different locations as well as the exposure class ofthe location. The exposure class affects the wind profile by multiplyingthe wind speed by a factor (e.g., 0.5 due to a coastal area exposureclass). To determine the appropriate factor, a lookup table indexed bylocation may provide a published wind speed and the appropriate factorto utilized based on exposure class. In other words, embodiments of theinvention may automatically retrieve a wind speed for a location,determines an appropriate factor, and then automatically adjusts thewind speed by the factor.

The simulated wind flow/pressures may then be presented to the user viaa color results map (overlaid onto/integrated with the structure) wheredifferent colors represent different pressures on the surface of thestructure. Such a color results map may be dynamically updated as thesimulation is conducted.

In order to perform an accurate analysis, a point of stability needs tobe reached with respect to the pressure generated. In this regard, eachtime an analysis is performed by the solver, a slightly different resultmay be output. In particular, even though computational fluid dynamicsmay be well understood, there is still an amount of chaos in ananalysis/results. However, over time and as different particles/elementsinfluence each other, the results from the solver begin to converge.

At step 308, a determination is made regarding whether convergence hasbeen achieved (e.g., if results are no more than 1% different [or withina range set by the user] in terms of a computational fluid dynamics(CFD) analysis). If the results of the wind flow simulation do notconverge, the process returns to step 306 for further wind flowsimulation. Further details regarding the convergence determination areset forth below.

Once convergence has been achieved, the process proceeds at step 310where the pressure is converted to loads on the structural elements.

At step 312, load cases are generated with the equivalent loads on theelements. Details regarding the generation of load cases are set forthbelow. Such a step is performed automatically based on thesolver/computational fluid dynamics analysis. Such load cases may beexported/saved to a file/spreadsheet/table that can be accessed by astructural engineer for further analysis/use. Such analysis/use mayinclude displaying a graphical representation of the load cases,actually building/constructing the physical structure/solid model basedon the load cases, etc.

Wind Load Simulation Exemplary Graphical User Interface

Several assumptions may be taken into account for simulating wind andgenerating wind loads:

A user should be able to see a wind flow preview during a simulationprocess;

Wind loads should be generated automatically (i.e., without additionaluser input);

A user should be able to generate wind loads at any time during asimulation process;

A system should be able to generate wind loads consecutively for a setof wind directions;

A user should be able to follow a simulation process;

A user should be able to stop a simulation process at any time; and

There should be an automatic pre-selection of elements that are windexposed.

Wind simulation may be possible in/from a structural analysisapplication via various methods. In a first method, an internal solver(i.e., within the structural analysis application) may be utilized togenerate wind load directly in the application. Using an internalsolver, the simulation process may be predefined and a user has limitedpossibilities to change simulation parameters. In a second method, amodel is provided to a CFD application for advanced analysis.

When a user elects to generate wind loads, a dedicated view of a wholestructure may be opened with elements that are wind exposed (wind loadscarrying) highlighted. In addition, a dedicated dialog comprisinginitial options and the ability to observe the simulation process andloads generation may be displayed.

FIGS. 4A and 4B illustrate various window tabs of an exemplary dialogthat may be used to set wind simulation parameters in accordance withone or more embodiments of the invention. The dialog 400 may open in abasic form with a left side folded. FIG. 4A illustrates the setup forestablishing/defining general parameters. The wind direction 402 (e.g.,in a global coordinate system) provides the ability for the user tochoose several wind directions (according to main axes and diagonals).If there is more than one direction chosen, a consecutive simulation maystart when wind loads are created for a previous direction. As adefault, there may always be an x+ direction chosen when the dialog isopened.

Wind parameter area 404 provides the ability to define the windintensity by wind velocity or wind pressure. The terrain level refers tothe ‘z’ global coordinate and indicates the level zero for a groundaround a building/model. A default value may be ‘0’ (zero) according toa global z-coordinate. This setting is a bottom limitation for a virtualbounding box for a wind simulation. In other words, the terrain levelcreates the bottom bounding plane for the structure to be analyzed. Anypart of the structure below the terrain level would not beanalyzed/accounted for in the wind analysis as it would be considered asub-surface structure.

Wind exposed elements area 406 provides the ability to identify a listof elements that are wind loads carrying. The list may be automaticallypopulated and can be edited by the user via a selection of elements inthe model (e.g., on a graphical viewer). The “Auto” button 408 enablesthe user to get back to the list of elements populated automatically(i.e., the default and/or initial pre-selection of elements). Theopenings in panels field 410 (mainly walls) allows the user to specifywhether such panels should be treated as closed or opened for a windsimulation (e.g., with a default of “closed”).

Loads generation area 412 provides options for generating loads based onthe wind flow. The first option is an automatic procedure based on aconvergence metric. This approach is based on a changeability study ofresultant forces calculated for different directions for the model. Thesecond option is a manual approach where it is assumed that a userdecides when to stop a wind simulation and generate adequate loads. Adefault value may be the automatic loads generation with a deviationfactor of 1%.

FIG. 4B illustrates an exemplary wind profile tab for definingparameters for the wind simulation. As a default, the wind flowintensity may be set as constant along a structure's height. A user canhowever change a wind velocity/pressure by defining a multiplier to abasis value. The multiplier (wind coefficient) is set on a graph 414 bydragging appropriate points (e.g., points 416). Points are located onparallel lines. Values on the abscissa (horizontal line) may be 1, 2, 3,4, while values on the ordinate (vertical line) may be 10, 15, 20, 25,30, 35, 40, 45, 50. The reset button 418 is to get back to a constantvalue of the wind flow (a multiplier/wind coefficient is set as “1”along the structure's height). To save a wind profile defined on thegraph, a name can be inputted in the text field 420 and the save button422 clicked. Thereafter, a saved wind profile may be loaded usingcombobox 424 and the load button 426. The name of the current windprofile may be displayed above the graph 414.

Once parameters have been established, the wind simulation process maystart (i.e., step 304 of FIG. 3) (e.g., via clicking the start button428). Once the simulation begins, a monitor part of the wind simulationdialog may unfold. The wind simulation progress monitor is illustratedin FIG. 5. There are two areas with general information about thesimulation and loads generation progress. The top part 502 and bottompart 504 of the dialog are used for these purposes.

The name of the current wind simulation is located at the top of thewindow. The name may be predefined and contains a fixed text “WindSimulation” and the rest depending on a direction and a windvelocity/pressure:Wind Simulation{direction}_{velocity/pressure value}

The same name may be automatically set as a name of an adequate loadcase created in the program.

The time of a current simulation may also be displayed in second(s).

In the bottom part 504 (i.e., “Process Status”), the steps performed areshown in a listbox. Different icons may reflect “In Progress”, “Done”,“Waiting”, and “Failed”.

The resultant forces area 506 display the forces acting on a structurethat are calculated during the simulation time for the main threedirections:

according to the wind direction (Wind compatible);

perpendicular to the wind direction (Perpendicular);

in vertical direction, according to the global ‘Z’ coordinate(Vertical);

During a simulation process, each resultant force is calculated in timeintervals. By comparison of forces values in following time steps, adeviation factor is calculated. A user may decide a reference value ofthe deviation factor (changeability of loads generated on elements). Thevalue is set in the main dialog window (a metric) (i.e., in area 412 ofFIG. 4A). The value specified in area 412 is set as a reference on theconvergence graph 508. All values above the set reference level may beshown in a first color (e.g., red). Values below may be displayed in asecond color (e.g., green). It may be assumed that all resultant forcesshould be below the set reference value to automatically generate loadsbased on the metric.

The maps display area 510 provides the ability to configure thepresentation of the wind simulation flow in the simulation application.Wind simulation flow may be presented by displaying wind velocity and/ordisplaying pressure generated by wind on structure members. The windvelocity may be presented on three independent planes, according to theglobal coordinate system. The velocity map may be flat but animatedduring a simulation process. The scale may be predefined. The pressuremay be displayed directly on an element's face. A map scale can beadjusted in a dedicated dialog accessible using the “Pressure scale”button 512.

At any given time, the user may opt to create loads on elements(members) based on the current wind simulation conditions (i.e., byselecting the “Generate loads now” button 514). Depending on the currentsimulation step and already existing load cases, the generating loadsprocess may be preceded by some warning/info message.

Wind Loads Simulation Convergence

At set forth above in FIG. 3, steps 306 and 308 determine when computedpressures on the surfaces of a model (based on wind simulation providedby a solver) converge. It may be noted that wind simulation is a dynamicprocess, changing in time. To track the process and its convergence,some metric is required to reflect the process state. This metric shouldbe constructed in such a way that different model sizes (high-risebuilding vs. single-family house) and different modes of the wind flowexposure (buildings with exterior façade vs. open models like highvoltage pole or offshore drilling platform) are supported.

Transient solvers often never provide totally stable results consideringall local pressure changes. However, structural engineers really needstable resulting loads on a structure model. Accordingly, instead of atotally stable system, embodiments of the invention examine convergewind simulation results to within a certain range.

Total Forces

The basic idea is to measure resulting total forces convergence in sometime period. Three values are monitored:

-   -   Fx_(wind) Total force in wind direction;    -   Fy_(wind) Total force in horizontal direction and perpendicular        to wind direction; and    -   Fz_(wind) Total force in vertical direction.

Scaling Forces

Total forces' values depend on model size. In order to fulfill themetric stability requirement, some relative values need to becalculated. To properly scale resultant forces one may use:

-   -   Dynamic pressure q=½ρv ²    -   Surface Sx_(wind) is obtained by projecting all triangles passed        to the simulation to a plane perpendicular to the x_(wind) (wind        direction) and calculating the area covered by them. Surface        Sy_(wind) is obtained by projecting triangles to the plane        perpendicular to the y_(wind) direction, and Sz_(wind) is        obtained by projecting triangles to the plane perpendicular to        the z_(wind) direction and calculating covered areas        respectively.    -   Sx_(wind), Sy_(wind) and Sz_(wind) values are used for scaling        corresponding force. This approach allows for the neutralization        of disproportions of the model in wind x, y and z directions.

Scaling Forces:Fx _(scaled) =ρv ² Sx _(wind)Fy _(scaled) =ρv ² Sy _(wind)Fz _(scaled) =ρv ² Sz _(wind)

Metric-Assessment of Resultant Forces Stabilization

The history of Fx_(wind), Fy_(wind), Fz_(wind) for N steps (which couldbe also converted to simulation time) is calculated and stored.

For the given simulation moment, a maximum change of each of theseforces is calculated for N previous stepsΔFx _(wind)=max(|Fx _(wind) −Fix _(wind)|)ΔFy _(wind)=max(|Fy _(wind) +Fiy _(wind)|)ΔFz _(wind)=max(|Fz _(wind) −Fiz _(wind)|)(where Fix_(wind), Fiy_(wind), Fiz_(wind) represent stored values ofFx_(wind), Fy_(wind), Fz_(wind) for a given step respectively—For i=1 toN).

These maximum force changes are now scaled by

Fx_(scaled), Fy_(scaled) Fz_(scaled) respectively and displayed as apercentage.ΔFx _(scaled) =ΔFx _(wind) /Fx _(scaled)ΔFy _(scaled) =ΔFy _(wind) /Fy _(scaled)ΔFz _(scaled) =ΔFz _(wind) /Fz _(scaled)

The final metric is the maximum of these three scaled valuesΔF _(scaled)=max(ΔFx _(scaled) ,ΔFy _(scaled) ,ΔFz _(scaled))

In order for the metric to be fully valid, at least N steps of thesimulation must be performed.

Metric Parameters

There are two parameters used in the above-described metric. As a resultof many experiments, values of these parameters may be:

-   -   N=10—Number of steps to store Fx_(wind), Fy_(wind), Fz_(wind)        values for    -   ΔF_(scaled)=0.5% —stable loads indicator        Wind Loads Simulation—Load Case Generation Assumptions

As described above, once results from a wind simulation convergence, theoutput are the pressures on the structural elements (e.g., that may beprovided in terms of a pressure map). Thereafter, steps 310-312 providefor converting the pressure/pressure map to loads and generating loadcases that may be utilized for further analysis. The generation ofloads/load cases based on an actual pressure map is a complex process.

The primary method to generate loads is a direct conversion of pressureon surfaces to loads applied to elements. A secondary method is togenerate a uniform load on elements or subparts of elements. This is anapproximate method, but its advantage is easy verification andcomparison with analytical methods. Embodiments of the invention are notlimited to any particular method for converting the pressures to loadson the structural elements.

Various assumptions may be established for generating the uniform loadsunder the secondary method:

-   -   Loads are generated as uniform loads (both on linear and planar        elements) equivalent to an average value of a pressure        calculated for a specific element;    -   Loads with the same value (intensity) are grouped together to        limit load records in the program; and    -   Additional linear loads distributed on panels' edges may be        generated in case of big pressure differences over a panel's        surface.

Linear Loads on Panels' Edges Generation Method.

FIG. 6 illustrates the different edges and panels that may be used tocompute linear loads in accordance with one or more embodiments of theinvention. In FIG. 6, A represents the main (internal) panel's area,B_(n) represents the edge area, and d represents the edge zone arearange. For each panel (a wall or a slab), a zone d along each edge maybe set internally. An average value of pressure is calculated in eacharea B_(n). To equilibrate a model, different edge loads may begenerated. FIG. 7 illustrates the equilibration of a model in accordancewith one or more embodiments of the invention.

If the average pressure value in an edge zone area B_(n) is sufficientlydifferent than the average pressure value in a main panel's area A, thenadditional edge loads are generated to counteract such a big difference(e.g., as illustrated at 702 and 704).

The average pressure difference may be calculated as:ΔP=|P _(A) −P _(Bn)|

-   -   where:    -   P_(A)—average pressure in the main (internal) area    -   P_(Bn)—average pressure in the zone area

The edge load generation condition may comprise:ΔP>a·q _(max)

-   -   where:    -   a—scale coefficient    -   q_(max)—maximum value of the dynamic pressure on a panel        q _(max)=½ρv ²    -   q—dynamic pressure in pascals    -   ρ—fluid density in kg/m³    -   v—maximum fluid velocity in m/s

The constants' values may be:

-   -   scale coefficient: a=0.3    -   edge zone area range: d=0.5 [m]

In case of different signs for the pressures in the main A and zoneB_(n) areas (positive vs negative) (e.g., as illustrated at 706), then ascale coefficient may be set to:a=0.03

If the edge loads generation condition is satisfied, then a linear edgeload is generated, and the value of the linear load is calculated toequilibrate a model (e.g., as illustrated at 708).

CONCLUSION

This concludes the description of the preferred embodiment of theinvention. The following describes some alternative embodiments foraccomplishing the present invention. For example, any type of computer,such as a mainframe, minicomputer, or personal computer, or computerconfiguration, such as a timesharing mainframe, local area network, orstandalone personal computer, could be used with the present invention.In summary, embodiments of the invention provide for the ability tosimulate wind flow using computational fluid dynamics. Further,embodiments of the invention, from within a structural analysisapplication, automate and present a process for analyzing flow patternsfrom multiple directions, and generate load cases for analysis. Such anapplication is flexible, is easy to obtain results for different windparameters, and is easy to determine preliminary wind effects early inthe design process. Further, in case of a change in a structure geometryor structure variants, a user can revise wind load effects quickly. Inaddition, embodiments of the invention are national code independent andcan be perceived as a virtual wind tunnel with automated loadsgeneration that provide significant time and cost savings to theengineer looking to understand the effects of wind and wind loads instructures.

The foregoing description of the preferred embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

What is claimed is:
 1. A computer-implemented method for automaticallysimulating a wind load, comprising: converting, in a computer, ananalytical model to a computer solid model by assigning parameters thatinfluence the wind flow to the computer solid model and automaticallygenerating a computer solid modeling façade for the analytical model,wherein: the parameters comprise identifying one or more of the elementsas open or closed; the computer solid modeling façade comprisesnon-structural elements that transfer the loads to a structural frame;and the analytical model comprises a geometric representation of astructural system; creating, in the computer, a virtual wind tunnel bysimulating a wind flow on the computer solid model to determinepressures on structural elements of the computer solid model; repeating,in the computer, the simulating until convergence of the pressures;converting, in the computer, the pressures to loads on the structuralelements; and generating, in the computer, load cases with equivalentload on the structural elements.
 2. The computer-implemented method ofclaim 1, further comprising: automatically generating a terrainassociated with the computer solid model, wherein the terrain affectsthe wind flow.
 3. The computer-implemented method of claim 1, whereinthe converting the analytical to the computer solid model furthercomprises: automatically generating icing by increasing a geometry ofthe computer solid model based on an icing condition.
 4. Thecomputer-implemented method of claim 1, wherein the simulating the windflow comprises: programmatically determining a bounding box around thecomputer solid model; defining wind parameters that describe a flow ofthe wind; and generating, via computational fluid dynamics, based on thebounding box and the wind parameters, the pressures on the structuralelements.
 5. The computer-implemented method of claim 1, wherein thesimulating is sequentially performed in multiple cardinal directions. 6.The computer-implemented method of claim 1, wherein the simulatingcomprises: defining a wind profile comprising different wind factors fordifferent wind directions and/or heights of the computer solid model,wherein the wind profile is used to simulate the wind flow.
 7. Thecomputer-implemented method of claim 1, wherein the simulatingcomprises: automatically configuring a wind profile that is dependent onterrain and an exposure category, wherein the wind profile is used tosimulate the wind flow.
 8. A non-transitory computer readable storagemedium encoded with computer program instructions which when accessed bya computer cause the computer to load the program instructions to amemory therein creating a special purpose data structure causing thecomputer to operate as a specially programmed computer, executing amethod of automatically simulating a wind load, comprising: converting,in the specially programmed computer, an analytical model to a solidmodel by assigning parameters that influence the wind flow to thecomputer solid model and automatically generating a computer solidmodeling façade for the analytical model, wherein: the parameterscomprise identifying one or more of the elements as open or closed; thecomputer solid modeling façade comprises non-structural elements thattransfer the loads to a structural frame; and the analytical modelcomprises a geometric representation of a structural system; creating avirtual wind tunnel by simulating, in the specially programmed computer,a wind flow on the computer solid model to determine pressures onstructural elements of the computer solid model; repeating, in thespecially programmed computer, the simulating until convergence of thepressures; converting, in the specially programmed computer, thepressures to loads on the structural elements; and generating, in thespecially programmed computer, load cases with equivalent load on thestructural elements.
 9. The non-transitory computer readable storagemedium of claim 8, further comprising: automatically generating aterrain associated with the computer solid model, wherein the terrainaffects the wind flow.
 10. The non-transitory computer readable storagemedium of claim 8, wherein the converting the analytical to the computersolid model further comprises: automatically generating icing byincreasing a geometry of the computer solid model based on an icingcondition.
 11. The non-transitory computer readable storage medium ofclaim 8, wherein the simulating the wind flow comprises:programmatically determining a bounding box around the computer solidmodel; defining wind parameters that describe a flow of the wind; andgenerating, via computational fluid dynamics, based on the bounding boxand the wind parameters, the pressures on the structural elements. 12.The non-transitory computer readable storage medium of claim 8, whereinthe simulating is sequentially performed in multiple cardinaldirections.
 13. The non-transitory computer readable storage medium ofclaim 8, wherein the simulating comprises: defining a wind profilecomprising different wind factors for different wind directions and/orheights of the computer solid model, wherein the wind profile is used tosimulate the wind flow.
 14. The non-transitory computer readable storagemedium of claim 8, wherein the simulating comprises: automaticallyconfiguring a wind profile that is dependent on terrain and an exposurecategory, wherein the wind profile is used to simulate the wind flow.